| A | B |
|---|
| gravity | Force between two objects with mass |
| orbit | Path of one object around another |
| solar system | the sun and everything that revolves around the Sun |
| galaxy | a system that is made up of billions of stars, star clusters and glowing clouds of dust and gas |
| universe | all of the galaxies and the space around them; everything in space |
| comet | their highly elliptical orbit prevents them from passing near Earth |
| Big Bang Theory | the theory that the universe was created by a huge explosion |
| Inertia | an object keeps moving or stays stationary until a force acts upon it |
| revolution | an object keeps moving around another object such as the Earth around the sun |
| rotation | a planet spinning on its axis; an object spinning in isolation |
| geocentric | the theory that Earth is the center of our solar system; it stated that the sun revolves around the Earth |
| heliocentric | the correct theory that the sun is the center of our solar system; Earth revolves around the sun |
| Ptolemy | astronomer who came up with the first theory about the universe; geocentric theory |
| Nicholas Copernicus | first astronomer who challenged the geocentric theory; came up with the heliocentric theory |
| Galileo | first to make and use the telescope |
| comet | chunks of ice and dust with long tails, called dirty snowballs |
| meteorites | Earth has craters formed by these |
| friction | force that causes meteoroids to burn up in the mesosphere |
| hydrogen | Gas giant's atmosphere is mainly formed of this gas |
| Viking | spacecraft that found regions on Mars which looked like streambeds |
| liquid water | liquid that is an important condition for life on Earth |
| Galileo Galilei | observed that Venus goes through phases like the moon |
| Galileo Galilei | observed moons around Jupiter |
| constellations | groups of stars |
| Mars | inner planet that may once had water on it's surface |
| mesosphere | layer of the atmosphere where meteoroids burn up |
| Milky Way Galaxy | galaxy our solar system resides in |
| extra-terrestrial | life on other worlds |
| asteroids | minor planets, too small to be a planet |
| spiral galaxy | galaxy with extending arms like a pinwheel |
| Goldilocks Condition | oceans, temperature, and atmosphere a it's three conditions |
| Earth | only planet with oceans |
| spiral galaxy | galaxy shaped like a pinwheel |
| Venus | planet called the "Evening Star" |
| Venus | planet with thick atmosphere that rains acid |
| Earth and Venus | two planet with Greenhouse Effect |
| meteoroid | was once a comet or asteroid or left over planet material |
| Jupiter | planet with a continuous storm, red spot |
| Mars | planet with rotation most similar to Earth |
| elliptical galaxy | galaxy that looks like a flattened ball or sphere |
| Venus | planet with the warmest all around temperature |
| Mars | red planet covered with Iron Oxide |
| Venus | planet whose rotation is longer than it's revolution |
| Saturn | planet with rings made of ice and rock |
| inertia and gravity | two forces which work together to keep the planets in their orbits |
| Tycho Brahe | scientist which made observations and charts of the planets orbits for 20 years |
| Johannes Kepler | scientist who studied chart and proposed elliptical orbits of the planets |
| meteor | streak of light produced by meteoroids burning in the mesosphere |
| Irregular galaxy | galaxy with an irregular shape |
| Magellanic Cloud | example of an irregular shaped galaxy |
| left corner 2/3 in a spiral arm | location of our solar system in the Milky Way galaxy |
| Big Crunch | future of our universe if gravity pulls the galaxies together |
| Gas Giants or Outer planets | planets much larger than Earth without a solid surface |
| Inner Planets or Terrestrial Planets | small planets with rocky surfaces |
| gravity | force which keeps the large atmosphere of the gas giants in place |
| asteroid belt | located between Mars and Jupiter |
| Uranus | most different from other planets since it rotates at a 97 degree angle on it's side |
| size and density | two factors that Earth and Venus are much alike |
| retrograde rotation | rotation from east to west |
| Elliptical Galaxy | galaxy which contains billions of old stars and not much gas and dust |
| Uranus and Venus | planets thought to have been struck by large asteroids and knocked off their tilt |
| Mars | planets named for the god of war |
| Venus | Earth's twin |
| Mars | planet with seasons like Earth |
| coma | atmosphere of a comet |
| Pluto | celestial body once a planet and now a dwarf planet |
| Ceres | celestial body once an asteroid in the asteroid belt but now a dwarf planet |
| Mars | Inner planet with two moons |
| Venus | brightest object in the western sky after sunset |
| Jupiter | planet with red spot - hurricane |
| Saturn | planet with the most visible rings - ice, rocks, and dust |
| Uranus | planet tilted on its side |
| Neptune | planet named for the god of the sea |
| rings | all gas giants are large, have moons, and these |
| methane | gas which causes Uranus and Neptune to appear blue |
| hydrogen | most abundant gas in the atmosphere of the gas giants |
| Oort Cloud | area outside our solar system from which comets come from |
| Halley's Comet | appears visible from Earth every 75 years |
| tail | Area of a comet which always faces away from the sun while orbiting |
| observatory | buildings used to see beyond Earth |
